Processes for removing oil from solid wellbore materials and produced water

ABSTRACT

Processes for removing oil from a solid wellbore material such as drill cuttings or water such as produced by a subterranean formation include contacting the solid material/water with an amino-substituted polymer such as chitosan and a halogenating agent. The oil separates from the solid material and becomes bound within a flocculated solid. The flocculated solid containing the oil subsequently may be combined with a solvent of the amino-substituted polymer. Further, the flocculated solid may be contacted with a reducing agent, converting the flocculated solid back into the amino-substitute polymer and forming an oil-phase separate from the solvent-phase. The oil-phase may then be separated from the solvent phase and recovered. The solvent in which the amino-substituted polymer is dissolved may be recycled for treating more solid material removed from the well bore.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional Application of U.S. patent application Ser. No.10/915,023, filed Aug. 10, 2004, now U.S. Pat. No. 7,192,527, andentitled “Processes for Removing Oil from Solid Wellbore Materials andProduced Water,” which is hereby incorporated by reference herein in itsentirety. The subject matter of the present application is also relatedto U.S. Pat. No. 6,846,420, issued on Jan. 25, 2005, and entitled“Process for Removing Oil from Solid Materials Recovered from a WellBore,” which is incorporated by reference herein.

FIELD OF THE INVENTION

This invention generally relates to oil/gas well drilling, cementing,and production operations. More specifically, the invention relates toprocesses for removing oil from solid materials such as drill cuttingsand sand removed from a well bore and from produced water.

BACKGROUND OF THE INVENTION

Well drilling is a process used in penetrating subterranean zones (alsoknown as subterranean formations) that produce oil and gas. In welldrilling, a well bore is drilled while a drilling fluid (also known as adrilling mud) is circulated through the well bore. The drilling fluid istypically an oil-based fluid comprising oils such as diesel, mineraloil, unsaturated olefins, and organic esters. After drilling the wellbore to a desired depth, a string of pipe, e.g., casing, is usually runin the well bore. The drilling fluid in the well bore may be conditionedby circulating it downwardly through the interior of the pipe andupwardly through the annulus, which is located between the exterior ofthe pipe and the walls of the well bore. Next, primary cementing istypically performed whereby a slurry of cement in water is placed in theannulus and permitted to set into a hard mass to thereby attach thestring of pipe to the walls of the well bore and seal the annulus.

During the drilling process, the drill bit generates drill cuttings asit forms the well bore. Drill cuttings consist of small pieces of shaleand rock. The drill cuttings are carried in a return flow stream of thedrilling fluid back to the well drilling platform. They are thenseparated from the bulk of the drilling fluid via conventionalseparators such as shale shakers, mud cleaners, and centrifuges. Someshale shakers filter coarse material from the drilling fluid while othershale shakers remove finer particles from the drilling fluid. Afterremoving the drill cuttings therefrom, the drilling fluid may be re-usedin the drilling process.

The drill cuttings separated from the bulk drilling fluid typically aredischarged from the drilling platform to the surrounding area. Drillingplatforms are often located offshore in hundreds of feet of water filledwith marine life. The drill cuttings thus accumulate in the seabed nearthe base of the platform. Unfortunately, the drill cuttings may becontaminated with the oil contained in the drilling fluid. This oil mustbe removed from the drill cuttings before their disposal to meetregulatory limitations. Otherwise, the oil would pollute the surroundingenvironment and would be particularly hazardous to marine life.

In addition, the crude oil recovered from the subterranean formationsoften contains sand that must be separated from the oil. Like the drillcuttings, the sand is disposed of by dumping it from the drillingplatform into the seabed where it forms sand piles. The sand also may beundesirably coated with the produced crude oil. Thus, the sand couldadversely affect the marine environment unless the oil is removedtherefrom.

Various methods have been used to remove oil from drill cuttings andsand, thereby meeting certain regulations designed to protect theenvironment from oil pollution. In one method, the oil is extractedusing solvents such as toluene or methylene chloride. However, thepotential hazards caused by the toxic nature of the solvents have raiseddoubts about this method. Another method involves transporting the drillcuttings and the sand onshore and subjecting them to a thermal process.Using such a thermal process can be very expensive, particularly sinceit is necessary to transport the drill cuttings and the sand to anonshore location.

An improved method has been developed to separate the oil from solidmaterial removed from a wellbore, such as drilling cuttings and sand. Inthis method, the solid material is passed from the well bore to aseparation zone located on or near the drilling platform, thus avoidingthe high costs associated with transporting the solid material onshore.Chitosan, water, and a halogenating agent such as bleach are introducedto the separation zone containing the solid material, leading to theformation of a flocculated solid that surrounds oil droplets. As aresult, the oil becomes trapped in the flocculated solid such that it isno longer disposed on the solid material. The solid material can then beseparated from the flocculated solid and discharged from the drillingplatform without being concerned that the surrounding environment couldbe harmed.

To avoid contaminating the environment with the oil contained in theflocculated solid, the flocculated solid can be collected and properlydisposed. It may be transported to an onshore location and incineratedat relatively high temperatures. The costs of transporting theflocculated solid and incinerating it and the oil bound therein can berelatively high. Thus, it is desirable to separate the oil from theflocculated solid such that the oil may be recovered, thus avoiding theproblems associated with its disposal. A need therefore exists for anenvironmentally friendly, economical, and simple method of recoveringthe oil from the flocculated solid.

SUMMARY OF THE INVENTION

Oil may be removed from a solid material (e.g., drill cuttings)recovered from a well bore or from water such as produced by asubterranean formation by contacting the solid material/water with apolymer substituted with an amino group such as chitosan and ahalogenating agent such as sodium hypochlorite. As a result of suchcontact, at least a portion of the oil separates from the solidmaterial/water and becomes bound within a flocculated solid formed fromthe polymer. The flocculated solid containing the oil may then becombined with a solvent of the polymer substituted with the amino group.Further, the flocculated solid may be contacted with a reducing agent,resulting in the removal of the oil from the flocculated solid and theformation of an oil-phase separate from the solvent-phase. The oil-phasemay then be separated from the solvent phase and recycled in, e.g., adrilling fluid, or recovered as product. In an embodiment, a process forrecovering oil disposed on a solid material removed from a well bore isdisclosed. The process comprises flocculating a polymer substituted withan amino group with a halogenating agent to bind the oil anddeflocculating the polymer with a reducing agent to release the oil.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Processes for recovering oil disposed on a solid material taken from awellbore first involve removing the oil from the solid material. Thisseparation of the oil may be accomplished by passing the solid materialfrom the well bore to a separation zone and introducing water, a polymersubstituted with an amino group (hereinafter “amino-substitutedpolymer”), and a halogenating agent to the separation zone. Optionally,one or more surfactants may also be introduced into the separation zone.Examples of solid materials to which such processes may be appliedinclude drill cuttings carried from a well bore via a stream of drillingfluid and sand carried from a well bore via a stream of crude oil.Before carrying out the oil recovery processes described herein,separation techniques known in the art could be used to separate thedrill cuttings from the bulk drilling fluid or the sand from the bulkcrude oil.

The separation zone may be disposed in processing equipment suitable forcombining the components as described herein, such as vessels, tanks,mixers, conveyors, and combinations thereof. The separation zone ispreferably disposed within a settling tank. The components may becombined and mixed in any sequence yielding the desired resultsdescribed herein. Suitable operating conditions for the separation zone,e.g., the operating temperature and pressure, would be obvious to thoseskilled in the art.

In an embodiment, the solid material is loaded into the separation zone,and the surfactant, the water, the amino-substituted polymer, and thehalogenating agent are subsequently combined and mixed, preferably inthe order indicated. The aqueous particle suspension formed prior to theaddition of the halogenating agent is vigorously mixed. In anotherembodiment in which a surfactant is not used, water is initially chargedto the separation zone, to which the solid material, amino-substitutedpolymer, and halogenating agent are added. Alternatively, one or moresurfactants may be added to the water along with the other components.In yet another embodiment, the solid material is coated with thesurfactant by, for example, spraying the surfactant on the solidmaterial or mixing the solid material in the surfactant. The solidmaterial is then vigorously mixed with water in the separation zone,followed by the addition of the amino-substituted polymer and thehalogenating agent while mixing.

After the addition of all of the components to the separation zone, thepH of the final mixture may be adjusted to a value in the range of fromabout 3 to about 7 by the addition of suitable acids or bases. Themixture is then agitated while the amino-substituted polymer reacts withthe halogenating agent, thus ensuring that the product of the reaction(i.e., an aminohalide polymer) is formed in intimate contact with thesolid material. The mixture is then allowed to stand for a period oftime sufficient to remove at least a portion of the oil from the solidmaterial. For example, depending on the halogenating agent used, themixture may be allowed to stand for a period sufficient to allow forsuspension of a newly formed flocculated solid. Three phases form as aresult of this process: an aqueous phase that is substantially free ofthe oil; the solid material having a reduced amount of oil thereon; andone or more flocculated solids in which the oil removed from the solidmaterial is bound. The solid material usually settles to the bottom ofthe aqueous phase while the flocculated solids float near the top of theaqueous phase. The amount of oil present in the solid material desirablymeets government regulations, thus allowing it to be disposed of onsite.In an embodiment, the foregoing process for removing the oil from thesolid material may be repeated as many times as necessary to reduce theamount of oil to within government regulations. Accordingly, the solidmaterial being disposed of preferably contains no greater than about 8%oil based on the weight of the solid material, more preferably nogreater than about 3% oil, and most preferably no greater than about 1%oil.

Without intending to be limited by theory, it is believed that the oilis removed from the solid material via the formation of one or moreflocculated solids. As used herein, “flocculated solid” refers to astructure comprising an aggregation of charged dispersed particlescaused by the reduction of the charge on each dispersed particle. Theflocculated solids are formed as a result of the amino (e.g., NH₂—)substituted polymer being oxidized by the halogenating agent. Thus, thehalogenating agent serves as an oxidizing agent that causes the hydrogenin the N—H bonds of the amino groups to be replaced with theelectronegative atoms (e.g., oxygen, nitrogen, or a halogen such asfluorine or chlorine) of the halogenating agent. Unlike theamino-substituted polymer, the flocculated solids are insoluble in theaqueous phase. The flocculated solids are also less dense than water andthus float at or near the surface of the aqueous phase.

The amount of water introduced to the separation zone may be effectiveto provide a total volume of liquid components (e.g, water, surfactant,amino-substituted polymer, and halogenating agent) sufficient tothoroughly wet, and preferably submerge, the solid material present inthe separation zone. In an embodiment, the water is fresh water. Theamount of the amino-substituted polymer introduced to the separationzone is effective to remove substantially all of the oil from the solidmaterial. For example, the amount of the amino-substituted polymer mayrange from about 0.3% to about 30% by weight of the solid material,alternatively from about 0.5% to about 10% by weight of the solidmaterial. Examples of suitable amino-substituted polymers includepolyvinylamine, polyalkyleneimines such as polyethyleneimine andpolypropyleneimine, polylysine, polymyxin, chitosan, a copolymer ofvinylamine and vinylalcohol, and combinations thereof.

In a preferred embodiment, the amino-substituted polymer is chitosan,which is a non-toxic, biodegradable polymer. Chitosan is derived fromchitin, which is a naturally-occurring polymer ofbeta-1,4-(2-deoxy-2-acetamidoglucose). Chitin is a primary constituentof the supporting tissues and exoskeletons of anthropods and insects andthe cell walls of many fungi. Living organisms, particularly seacrustacea such as crabs, shrimps, and lobsters, produce millions of tonsof chitin every year. Chitosan is derived from chitin by hydrolysis ofsome 2-deoxy-2-acetamidoglucose units to 2-deoxy-2-aminoglucose units.The term “chitosan” generally refers to copolymers having greater than65% 2-deoxy-2-aminoglucose monomeric units, with the remainder monomericunits being 2-deoxy-2-acetamidoglucose units. The chitosan preferably isdissolved in an aqueous acidic solution before introducing it to theseparation zone. A preferred aqueous acidic solution comprises about 1%acetic acid based on the combined weight of the acetic acid and thewater. A preferred chitosan solution is poly N-acetylglucosamine, whichis at least 65% deacetylated, dissolved in an acetic acid solution.Alternatively, chitosan in the solid form may be purchased from VansonCompany of Redmond, Wash, USA under the tradename KLARIFY 101. Withinthe separation zone, the chitosan is present in the aqueous acidicsolution as a polycation with the protonated amino group bearing apositive charge. The protonated amino group bonds with the halogenprovided by the halogenating agent, thus becoming less polar. As aresult of the reaction of the chitosan with the halogenating agent, atleast a portion of the 2-deoxy-2-aminoglucose monomeric units of thechitosan are converted to 2-mono or 2,2-dihalo aminoglucose monomericunits to yield a new polymer known as N-halochitosan. To optimize therate of reaction and to minimize the decomposition of the N-halochitosanproduct, the separation zone is maintained at a temperature preferablyin the range of from about 0° C. to about 80° C., and more preferably inthe range of from about 15° C. to about 30° C. Additional disclosureregarding the preparation of N-halochitosans can be found in U.S. Pat.No. 5,362,717; and U.S. Pat. No. 5,204,452, which are incorporatedherein in their entirety.

In an alternative embodiment, the amino-substituted polymer ispolyethylenimine. In an embodiment, the polymer comprises branchedpolyethylenimine obtained by polymerizing aziridine. In anotherembodiment, the polymer comprises non-branched polyethylenimine. When apolyethylenimine solution in water is used, it is preferably reactedwith the halogenating agent prior to the adjustment of pH to prevent theprecipitation of the former at acidic pH.

A halogenating agent or combination of halogenating agents suitable forreacting with and halogenating or oxidizing the amino-substitutedpolymer to form a haloamino polymer may be used. As used herein,“halogenating agent” refers to a compound having a halogen bound to astrongly electronegative atom such as oxygen, nitrogen, or another moreelectronegative halogen such as fluorine. The halogenating agent ispreferably introduced to the separation zone in an amount effective toachieve from about 30% to about 100% conversion of the amino-substitutedpolymer. Examples of suitable halogenating agents include sodiumhypochlorite, calcium hypochlorite, chlorine, bromine,N-chlorosuccinimide, sodium hypobromite, pyridinium bromide perbromide,N-bromosuccinimide, chloramine-T, and combinations thereof. In preferredembodiments, the halogenating agent is sodium hypochlorite, which isreadily available and relatively inexpensive. The sodium hypochlorite ispreferably introduced to the separation zone in an aqueous solution.When sodium hypochlorite is reacted with chitosan to formN-halochitosan, the reaction is usually complete in less than aboutabout 10 minutes. Less reactive halogenating agents such asN-bromosuccinimide may require about 30 to 60 minutes, or even longerdepending on the temperature, to complete the reaction.

In an alternative embodiment, a surfactant or combination of surfactantssuitable for promoting the removal of oil from the solid material may beused. By way of example, the amount of surfactant introduced to theseparation zone may range from about 0.1% to about 20% by weight of thesolid material, from about 2% to about 15% by weight of the solidmaterial, or from about 3% to about 10% by weight of the solid material.The surfactant may be nonionic, anionic or cationic; however, anon-ionic surfactant is preferred. The ability of a surfactant toemulsify two immiscible fluids, such as oil and water, is oftendescribed in terms of hydrophile-Lipophile balance (HLB) values. Thesevalues, ranging from 0 to 40, are indicative of the emulsificationbehavior of a surfactant and are related to the balance betweenhydrophilic and lipophilic portions of the molecules. In general,surfactants with higher HLB values are more hydrophilic than those withlower HLB values. As such, they are generally more soluble in water andare used in applications where water constitutes the major or externalphase and a less polar organic fluid constitutes the minor or internalphase. Thus, for example, surfactants with HLB values in the range 3-6are suitable for producing water-in-oil emulsions, whereas those withHLB values in the 8-18 range are suitable for producing oil-in-wateremulsions. A commonly used formula for calculating HLB values fornonionic surfactants is given below:HLB=20×M _(H)/(M _(H) +M _(L))where M_(H) is the formula weight of the hydrophilic portion of themolecule and M_(L) is the formula weight of the lipophilic portion ofthe molecule. When mixtures of surfactants are used, the overall HLBvalues for the mixture are calculated by summing the HLB contributionsfrom different surfactants as shown in equation below:HLB=({acute over (ø)}₁ ×HLB ₁+{acute over (ø)}₂ ×HLB ₂+ . . . + . . .etc.,)where {acute over (ø)}₁ is the weight fraction of surfactant #1 in thetotal mixture, HLB₁ is the calculated HLB value of surfactant #1, {acuteover (ø)}₂ is the weight fraction of surfactant #2 in the totalsurfactant mixture, and HLB₂ is the calculated HLB value of thesurfactant #2, and so on.

It has been observed that a mixture of a preferentially oil-solublesurfactant and a preferentially water-soluble surfactant provides betterand more stable emulsions. As such, these types of mixtures may be usedto further reduce the oil-content on the solid material. In particular,non-ionic ethoxylated surfactant mixtures containing from about 3 toabout 12 moles of ethylene oxide, exemplified by nonylphenol ethoxylatescontaining from about 4 moles to about 10.5 moles of ethylene oxide arepreferred. The HLB ratio for a single surfactant or a surfactant mixtureemployed to assist in the removal of the oil preferably ranges fromabout 7 to about 16, more preferably from about 8 to about 15.

The recovery of the oil previously disposed on the solid material nextinvolves separating the aqueous phase, the solid material, and the oneor more flocculated solids. Suitable separation techniques would beknown to those skilled in the art. For example, the flocculated solidsmay be skimmed from the top of the aqueous phase, followed by decantingthe aqueous phase, thereby leaving behind the solid material in a wetstate. Devoid of the oil, the solid material may be discharged from thedrilling platform without being concerned that the surroundingenvironment could be harmed. Alternatively, it may be disposed of in alandfill.

The oil bound within the flocculated solids may then be removed bycombining within a separation zone the flocculated solids with areducing agent and a relatively good solvent of the amino-substitutedpolymer previously used to form the solids. Suitable solvents arecapable of dissolving the amino-substituted polymer and are immisciblewith oil. The flocculated solids, the reducing agent, and the solventmay be introduced to the separation zone in any sequence or combination.The reducing agent may be introduced to the separation zone directly orin a solution such as an aqueous solution, which may contain a minisculeamount of the reducing agent up to a saturated amount of the reducingagent. Examples of suitable reducing agents include ascorbic acid;alkali metal and ammonium salts of sulfite, bisulfite, dithionite,metabisulfite, and thiosulfate anion; sodium borohydride; potassiumborohydride; sodium triacetoxyborohydride; potassiumtriacetoxyborohydride; and combinations thereof. The solvent may be, forexample, water and is preferably acidic water containing organic acidssuch as acetic and lactic acids. The volume of solvent placed in theseparation zone is sufficient to thoroughly wet and preferably submergethe flocculated solids.

The separation zone employed for recovering the oil from the flocculatedsolids may be contained within processing equipment suitable forcombining the above components, such as vessels, tanks, mixers,conveyors, and combinations thereof. The separation zone is desirablydisposed in a stirred tank equipped with outlets to skim off the oil anddrain the aqueous layers. While agitating the materials therein, theseparation zone is maintained at operating conditions suitable forcausing the flocculated solids to be reduced by the reducing agent. Inan embodiment, the separation zone is maintained at atmospherictemperature and pressure. The reduction of the flocculated solidsthereby converts them back into an amino-substituted polymer in whichthe amino groups are bonded to hydrogen rather than electronegativeatoms. As such, at least a portion of the flocculated solids disappears,and the amino-substituted polymer that forms becomes dissolved in thesolvent. Further, the oil that had been bound within the flocculatedsolids forms its own oil-phase separate from and above thesolvent-phase. If all of the flocculated solids have not disappeared,additional amounts of the reducing agent may be introduced to theseparation zone. The total amount of the reducing agent introduced tothe separation zone is effective to release all of the oil from theflocculated solids, as indicated by the disappearance of substantiallyall of the flocculated solids.

If desired, surfactants which can de-emulsify or lower interfacialtension (IFT) among dispersed oil droplets to cause coalescence of theoil droplets may optionally be introduced to the separation zone toimprove the separation between the oil-phase and the solvent-phase byinhibiting or reducing the formation of an interface layer comprising anoil/solvent emulsion. Additionally, salt may be optionally added toaugment the oil/water separation and to enhance the performance of thesurfactants. Examples of suitable surfactants include alcohol ethersulfates in which the hydrophobic group may comprise linear or branchedalkly groups or alkylated aryl groups, alkylated diphenyletherdisulfonates, alpha-olefin alkylaryl sulfonates, and combinationsthereof. Examples of such surfactants that are commercially availableinclude: NEA-96, MOREFLO, AS-10, and LOW SURF 300, all available fromHalliburton Energy Services, Inc.; DOWFAX 8390 available from DowChemical Company; and ISOFOL 145-4PO available from Condea Vista Companyof Houston, Tx. The amounts of the de-emulsifying or IFT reducingsurfactant and/or salt introduced to the separation zone is preferablysufficient to achieve a clean separation of the oil-phase and thesolvent-phase such that the oil/solvent interface layer is minimized.

The oil-phase may be separated from the solvent-phase using knownseparation techniques for separating immiscible liquids. For example,the oil-phase may be skimmed off of the solvent-phase or decanted.Alternatively, the solvent-phase may be drained out of the bottom of thevessel or tank in which it is contained. The oil may be recoveredwithout having to perform difficult purification steps on the oil, whichcan be used for various purposes including the formation of an oil-baseddrilling fluid. The oil can also be recovered as product. Moreover, thesolvent containing the amino-substituted polymer also can be recycledfor use in removing yet more oil from solid material recovered from awellbore, such as drill cuttings and sand. Recovering the oil in themanner described above is therefore efficient and economical. It alsoeliminates the need to dispose of the oil properly in accordance withgovernment regulations.

The processes described above for removing oil from solid materials maybe followed to also remove oil from water, for example water producedfrom a subterranean formation, with the exception that additional waterneed not be introduced to the separation zone. Such water may beproduced along with oil that is being recovered from a well thatpenetrates a subterranean formation. The water is more likely to beproduced after the well matures and oil has been recovered therefrom fora relatively long period of time. The water may also be contained in oilrecovered as a result of stimulation operations such as fracturing andacidizing.

After contacting the water with a polymer substituted with an aminogroup and a halogenating agent to cause at least a portion of the oil tobecome bound within a flocculated solid, the processes described abovefor separating the water, the flocculated solid, and the oil may also beapplied. That is, the flocculated solid may be combined with a solventof the polymer substituted with the amino group. As a result, at least aportion of the oil separates out into an oil-phase. The water from whichthe oil is removed may be used for various purposes or disposed ofwithout being concerned that it could contaminate the environment. Itmay contain from about 0.5% to about 20% oil by weight of the water.

EXAMPLES

The invention having been generally described, the following examplesare given as particular embodiments of the invention and to demonstratethe practice and advantages hereof. It is understood that the examplesare given by way of illustration and are not intended to limit thespecification or the claims to follow in any manner.

Comparative Example 1

A sample of a base oil used in a drilling fluid commercially availablefrom Halliburton, Inc. under the tradename ACCOLADE™ was obtained. Amilliliter of the oil was added to 100 milliliters (mL) of tap water,emulsified with high speed agitation for 1 minute, and set aside for 15minutes. An identical emulsion was prepared in a separate beaker and tothis emulsion, 10 mL of a 1 weight (wt.) % solution of chitosan preparedin a 1 wt. % acetic acid solution was added, stirred, and set aside. Athird batch of identical emulsion was prepared and 10 mL of the 1 wt. %chitosan solution was added while stirring, followed by adding 10 mL ofsodium hypochlorite solution (5 wt. % sodium hypochlorite solution istypically sold as household bleach). In 15-30 minutes, the beakercontaining chitosan and bleach solution contained white flocculatedsolid floating on completely clear water. The other two beakerscontained uniform milky emulsions. The milky emulsions were stable anddid not show any signs of separation even after 48 hours. The beakercontaining the flocculated solid was filtered, followed by drying thesolid at room temperature. A thermal gravimetric analyses (TGA) of thedried solid and of a sample of the oil was taken using a Hi-Res TGA 2950Thermogravimetric Analyser manufactured by TA Instruments of New Castle,Del., USA. The TGA showed that the filtered flocculated solid containedthe oil used in the emulsion.

Comparative Example 2

An emulsion identical to the one described in Comparative Example 1 wasprepared in 100 mL of water. Enough polyethylenimine concentrate (33 wt.% solution) was added to the emulsion with stirring, followed by adding10 mL of sodium hypochlorite solution to the emulsion and setting theresulting mixture aside. An identical mixture was prepared in a separatebeaker, and the pH of the mixture was lowered to 5.5 with glacial aceticacid. After about 18 hours, the beaker containing the emulsion mixtureat a lower pH showed flocculated solid floating in water, whereas thebeaker containing emulsion mixture at a higher pH did not show anytendency to form flocculated solid.

Example 1

A 20/40mesh (U. S. Series) graded sand was contacted with ACCOLADE™drilling fluid for several hours, followed by physically separating thesand from the drilling fluid. A sample of the sand, which was coatedwith the drilling fluid when tested by the TGA method, was found tocontain 10.3% volatiles by weight of the sand in the 25° C. to 500° C.range.

Another 1 gram sample of the sand contacted with the ACCOLADE™ drillingfluid was suspended in 100 mL of water and vigorously agitated for oneminute. A 10 mL sample of 1 wt. % chitosan solution in a 1 wt. % aceticacid solution was added while stirring, followed by adding 10 mL of ableach solution containing 5 wt. % sodium hypochlorite to induce theremoval of oil from the sand sample. After the oil in the sand samplehad been removed, the sand sample was collected by decantation. TGAanalysis of the collected sand showed that all the volatiles from thedrilling fluid had been removed by the treatment.

During the oil removal process, a suspended solid phase containing theoil removed from the sand sample was formed. The suspended solid phasewas tested by TGA to determine the amount of oil present in thesuspended solid phase. The results showed that the suspended solidcontained 56% by total weight of the oil removed from the sand. Thisamount accounts approximately for all the volatiles removed from thesand.

Comparative Example 3

A field sample of cuttings collected during drilling in the Chesapeakearea using a typical diesel based drilling fluid was obtained for use asa control sample. The control sample was then analyzed by TGA. Asindicated in Table 1 below, the TGA showed 15.3% volatiles by weight ofthe cuttings in the 75-200° F. range and 17.3% volatiles by weight ofthe cuttings in the 75-475° F. range.

Examples 2-9

In Example 2, the procedure used was identical to that used in Example 1with the exception of using a field sample of cuttings. In Examples 3and 5-9, one or more surfactants were added directly to the drillcuttings, followed by the addition of water with vigorous stirring,followed by the addition of the chitosan solution and bleach solution asdescribed in Example 1. In Example 4, Surfactant A was added to water,and the rest of the procedure was the same as described in Example 1.Surfactant A is a nonylphenol ethoxylate containing 4 moles of ethyleneoxide (calculated HLB value=8.8), and Surfactant B is a nonylphenolethoxylate containing 10.5 moles of ethylene oxide (calculated HLBvalue=13.6), both of which are available from Union Carbide Corporationas TERGITOL NP 4 and TERGITOL NP 10, respectively. Table 1 below showsthe amount of each surfactant added to the drill cuttings.

After treatment, the drill cuttings were separated from the aqueouslayer of the removed oil. Additional water was used to rinse thedecanted cuttings. The cuttings were dried at room temperature andanalyzed by TGA to determine the weight % of oil remaining aftertreatment. The results of the TGA analysis are also shown in Table 1.The volatile portion in the 75-200° F. range presented in Table 1represents the base oil present in the drilling fluid. Any materialvolatilized in the 200-475° F. range represents the drilling fluidcomponents, which are less volatile and typically consist of emulsifiersand calcium salts present in the internal aqueous phase. Such materialsare not considered particularly hazardous compared to the base oil. InTable 1, the total volatile content of the treated cuttings in the75-475° F. and in the 75-200° F. range are presented. A portion of thetreated cuttings were lost in the suspended solid because of theirextremely small particle sizes, which prevented their settling.

TABLE 1 Wt. % Oil Wt. % Residue Wt. % Total Total Surfactant ASurfactant B (volatile Wt. % Oil Residue Volatile (% by (% by Surfactantportion Reduction Volatized Reduction weight of weight of Applicationbetween on the between 75° Due to Example cuttings) cuttings Method75°-200° F.) Cuttings and 475° F. Treatment Control — — — 15.3 — 17.3 —(Untreated) 2 None None None 4.0 73 7.6 58 3 10 None Coat 3.2 79 13.9 204 10 None Solution 3.7 76 9.3 46 5 None 10 Coat 2.7 82 6.1 65 6 5 5 Coat1.0 93 4.6 73 7 2.4 0.6 Coat 2.3 85 6.2 64 8 8 2 Coat 4.0 74 13.3 23 9 28 Coat 0.93 94 4.8 72

The data in Table 1 indicates that the oil content of the treatedcuttings in Example 2 was reduced by 73 wt. % due to treatment withchitosan and bleach solution without using any surfactants. The overallreduction of the total volatile content of the treated cuttings inExample 2 was 58 wt. %. A comparison of the results from Examples 3 and4 suggests that the surfactant can be applied either in solution form oras a pre-coat on the cuttings prior to treatment with chitosan andbleach solution. The results indicate slightly better performance in oilreduction (see volatile content loss in 75-200° F.) when the surfactantis applied as a pre-coat. The results from Example 5 suggest that usinga surfactant with a higher HLB value, i.e., Surfactant B, is moreeffective in reducing both the oil content and the total volatilecontent when compared to Surfactant A in Example 3. The results fromExamples 6-9 also show that using mixtures of the two surfactants ismore effective than using each surfactant individually in similar orsignificantly reduced amounts.

Example 10

Some of the flocculated solid samples prepared in Comparative Example 1were collected by filtration and redispersed in an aqueous solutioncontaining 1% acetic acid by weight of the solution. Then 25 mL aliquotsof the suspension were placed in test tubes. Various reducing agentssuch as sodium bisulfite, sodium sulfite, or ascorbic acid werethereafter added to some samples, non-reducing agents such as citricacid or sodium bisulfate were added to other samples, and a surfactantsuch as LOW SURF 300 was added to some samples, e.g., sodium sulfite andLOW SURF 300. The test tubes were subjected to vigorous shaking, and thedisappearance of the flocculated solid and the appearance of the oillayer were observed. In the samples containing the reducing agents, theoil layer formed above the water layer. In the samples containing thenon-reducing agents, the oil and water remained mixed rather thanseparating into distinct layers. Surfactants such as LOW SURF 300surfactant available from Halliburton Energy Services, Inc. helped withthe phase separation in samples containing a reducing agent.

While the preferred embodiments of the invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit and teachings of the invention. Theembodiments described herein are exemplary only, and are not intended tobe limiting. Many variations and modifications of the inventiondisclosed herein are possible and are within the scope of the invention.Use of the term “optionally” with respect to any element of a claim isintended to mean that the subject element is required, or alternatively,is not required. Both alternatives are intended to be within the scopeof the claim.

Accordingly, the scope of protection is not limited by the descriptionset out above, but is only limited by the claims which follow, thatscope including all equivalents of the subject matter of the claims.Each and every claim is incorporated into the specification as anembodiment of the present invention. Thus the claims are a furtherdescription and are an addition to the preferred embodiments of thepresent invention. The discussion of a reference herein is not anadmission that it is prior art to the present invention, especially anyreference that may have a publication date after the priority date ofthis application. The disclosures of all patents, patent applications,and publications cited herein are hereby incorporated by reference, tothe extent that they provide exemplary, procedural or other detailssupplementary to those set forth herein.

1. A process for removing oil from water comprising: contacting the oiland water with a polymer substituted with an amino group and ahalogenating agent, thereby causing at least a portion of the oil toseparate from the water and become bound within a flocculated solidformed from the polymer; separating the flocculated solid from thewater; contacting the flocculated solid with a reducing agent to form anoil phase and an aqueous phase containing the polymer; and recoveringoil from the oil phase.
 2. The process of claim 1 wherein the polymersubstituted with the amino group comprises chitosan, polyvinylamine, acopolymer of vinylamine and vinylalcohol, polyethylenimine, polylysine,polymyxin, or combinations thereof.
 3. The process of claim 1 whereinthe halogenating agent comprises sodium hypochlorite, calciumhypochlorite, chlorine, bromine, N-chlorosuccinimide, sodiumhypobromite, pyridinium bromide, perbromide, N-bromosuccinimide,chloramine-T, or combinations thereof.
 4. The process of claim 1,wherein the reducing agent comprises ascorbic acid, an alkali metal orammonium salt of a sulfite, bisulfite, dithionite, metabisulfite, orthiosulfate anion, sodium borohydride, potassium borohydride, sodiumtriacetoxyborohydride, potassium triacetoxyborohydride, or combinationsthereof.
 5. The process of claim 1, wherein said contacting theflocculated solid with the reducing agent forms the polymer substitutedwith the amino group from the flocculated solid, and wherein at least aportion of the polymer substituted with the amino group dissolves in theaqueous phase.
 6. The process of claim 5, further comprising separatingthe oil, phase from the aqueous phase and recovering the oil phase. 7.The process of claim 6, further comprising recycling the water in whichthe polymer substituted with the amino group is dissolved, therebyremoving oil from a solid material recovered from a wellbore.
 8. Theprocess of claim 7, further comprising contacting the recycled watercontaining the polymer substituted with the amino group with a solidmaterial recovered from a wellbore and having oil disposed thereon. 9.The process of claim 1, further comprising introducing a de-emulsifyingor interfacial tension reducing surfactant to the aqueous phase toimprove the separation of the oil phase from the aqueous phase.
 10. Theprocess of claim 9, further comprising introducing a salt to the aqueousphase to enhance performance of the surfactant.
 11. The process of claim1, wherein the water is produced from a subterranean formation.
 12. Theprocess of claim 11, wherein the water is produced in conjunction with adrilling, cementing, or production operation.
 13. The process of claim12, wherein the drilling, cementing, or production operation is astimulation operation.
 14. The process of claim 13, wherein thestimulation operation is a fracturing or acidizing operation.
 15. Theprocess of claim 11, wherein the oil is produced with the water.
 16. Aprocess for recovering oil from water, comprising: flocculating apolymer substituted with an amino group with a halogenating agent toremove at least a portion of the oil from the water and bind the oil ina flocculated solid formed by the polymer, thereby causing at least aportion of the oil to separate from the water; forming an oil phase andan aqueous phase containing the amino-substituted polymer bydeflocculating the amino-substituted polymer by contacting theflocculated solid with a reducing agent; and recovering oil from theoil-phase.
 17. The process of claim 16, wherein the polymer substitutedwith the amino group comprises chitosan, polyvinylamine, a copolymer ofvinylamine and vinylalcohol, polyethylenimine, polylysine, polymyxin, orcombinations thereof.
 18. The process of claim 16, wherein thehalogenating agent comprises sodium hypochlorite, calcium hypochlorite,chlorine, bromine, N-chlorosuccinimide, sodium hypobromite, pyridiniumbromide, perbromide, N-bromosuccinimide, chloramine-T, or combinationsthereof.
 19. The process of claim 16, wherein the reducing agentcomprises ascorbic acid, an alkali metal or ammonium salt of a sulfite,bisulfite, dithionite, metabisulfite, or thiosulfate anion, sodiumborohydride, potassium borohydride, sodium triacetoxyborohydride,potassium triacetoxyborohydride, or combinations thereof.
 20. The methodof claim 16 wherein the oil and water are recovered from a subterraneanformation during a well servicing operation.